Complex composite structures and method and apparatus for fabricating same from continuous fibers

ABSTRACT

A method and apparatus for fabricating a complex, three-dimensional structure ( 12 ), such as a truss, from composite fiber/resin includes pulling a plurality of continuous fibers ( 50 ) from a feed source ( 62 ) along a processing path ( 58 ) about a longitudinal axis ( 14 ). At least some of the fibers are wound around the longitudinal axis in opposite directions ( 70,72 ) by rotational elements to form helical and reverse helical components ( 30, 34 ) that intersect at nodes ( 26,28 ). Select nodes are engaged by engagement members ( 84 ) and are maintained radially outwardly from the longitudinal axis by a support frame ( 80 ) to create sequential discrete segments ( 22 ) in the helical and reverse helical components. The select nodes can be engaged and maintained from outside the helical and reverse helical components. Resin can be applied to the fibers by resin applicator ( 90 ) and cured. A three-dimensional structure ( 200 ) can be formed with one or more continuous fibers forming two or more different components ( 204, 206 ) of the structure and transitioning at transition nodes ( 207 ). A three-dimensional structure can be formed with the components including a sleeve ( 162 ) of braided fibers surrounding a core ( 163 ) of elongated fibers to reduce gaps.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to complex, compositestructures and an apparatus and method for fabricating such complexstructures from composite fiber/resin. More particularly, the presentinvention relates to an apparatus and method for fabricating complexstructures with a plurality of helical and/or reverse helicalcomponents, such as trusses or cylinders.

[0003] 2. Related Art

[0004] Complex truss structures have been described in U.S. Pat. No.5,921,048 that can have enhanced load bearing capacity per unit weight.Such structures can have complex configurations, including for example,a plurality of helical components formed around a longitudinal axis inopposite directions. Each helical component can include a plurality ofsequential straight segments coupled end-to-end in a helicalconfiguration. Each helical component can include three segments forminga single, complete rotation about the axis, such that the helicalcomponent has a triangular cross-sectional shape formed by the straightsegments when viewed along the axis.

[0005] The plurality of helical components can include both 1)spaced-apart helical components formed around the axis in one directionor with one angular orientation, and 2) spaced-apart reverse helicalcomponents formed around the axis in another direction or with anopposing angular orientation. The straight segments of the helical andreverse helical components can form a triangular cross-sectional shapewhen viewed along the axis. In addition, the helical components furthercan include 3) spaced-apart rotated helical components, and 4)spaced-apart rotated reverse helical components, that are similar to therespective helical and reverse helical components, but rotated about theaxis with respect to the helical and reverse helical components. Thus,the helical and reverse helical components form a first triangularshape, while the rotated helical and rotated reverse helical componentsform a second triangular shape concentric with, but rotated with respectto, the first triangular shape, to form a six-pointed star shape.

[0006] The various helical components form a basic repeating patternalong the length of the structure. In addition, the various helicalcomponents intersect one another at internal and external nodes, withthe external nodes being spaced further from the axis than the internalnodes. For example, the helical and reverse helical components intersectat internal and external nodes. The structure further can include axialcomponents that extend along the length of the structure parallel withthe axis. Such axial components can intersect the helical components,including for example, at the internal and/or external nodes.

[0007] It is desirable to form such structure from composite materialsto reduce weight and increase strength. In addition, it is desirable toform the helical and axial components from continuous fibers to furthermaximize the strength of the structure. Thus, the fibers are traversingalong the structure at various angles. As stated above, such structureshave shown unexpected stiffness, and strength or load bearing capacityper unit weight.

[0008] The fabrication of such structures, however, has proven to bevery difficult. Wide-spread application of such structures has beenfrustrated by the inability to quickly, easily, and/or inexpensivelymanufacture such structure. It will be appreciated that such structureshave complex geometries or configurations. It also will be appreciatedthat such complex geometries have proven ill suited for conventionalmanufacturing techniques.

[0009] Various manufacturing processes exist for composite fiber/resin.For example, in a pultrusion process, the fiber and resin is extrudedand pulled through a die having the desired, continuous, cross-sectionalshape. As another example, braiding processes overlap fibers into a sockor sleeve configuration in a continuous, closed layer. Such sleeves canbe formed or disposed over a mandrel or around a die. As anotherexample, mandrel techniques wind fiber about a solid model or mandrelwith a continuous, solid outer surface having the desired configurationabout which the fibers are disposed. After the fiber has beenimpregnated with resin, and the resin cured to form a rigid structureabout the mandrel, the mandrel can be removed to leave the rigidstructure.

[0010] None of these existing technologies appears suited for continuousor volume manufacturing of such complex, three-dimensional structuresdescribed above. For example, it will be appreciated that the complex,three-dimensional nature of the structure, with the straight segmentsextending through the structure between external nodes, makes anymandrel shaped as the structure difficult to remove from the structureitself. Similarly, it will be appreciated that the complex,three-dimensional structure has a varying cross-sectional shape, anddiscontinuous or open surface structure, which is ill-suited forconventional pultrusion techniques. As another example, it is unclear,how braiding techniques could be used to fabricate more complex and openstructures, such as those described above.

[0011] In addition, the intersections of the various helical componentsat the nodes have also proven problematic. It will be appreciated thatas the various fibers intersect, gaps can be formed between the fiberswhich can reduce the strength of the structure by as much as 90 percent.

SUMMARY OF THEE INVENTION

[0012] It has been recognized that it would be advantageous to developan apparatus and/or method for fabricating complex structures, such asthose with complex helical configurations. In addition, it has beenrecognized that it would be advantageous to develop such structures toprevent or resist the formation of gaps between overlapping fibers.

[0013] The invention provides complex, composite three-dimensionalstructures and a method and apparatus for fabricating the complex,composite structures from continuous fibers. Such structures can includehelical and reverse helical components that wrap around a longitudinalaxis in opposite directions and intersect one another at nodes. Thehelical and reverse helical components can be formed of sequentialdiscrete segments. Additional longitudinal members can extend parallelto the longitudinal axis and intersect the nodes.

[0014] The method includes pulling a plurality of continuous fibers froma feed source along a processing path about a longitudinal axis. Atleast some of the fibers are wound around the longitudinal axis inopposite directions to form helical and reverse helical components thatintersect at nodes. The fibers are engaged in the processing pathsubstantially only at locations localized at select nodes withoutsubstantially engaging the helical and reverse helical components. Theselect nodes are maintained radially outwardly from the longitudinalaxis to create sequential discrete segments in the helical and reversehelical components. Resin is applied to the fibers, and cured.

[0015] In accordance with a more detailed aspect of the presentinvention, the method can further include engaging the select nodes fromoutside the helical and reverse helical components. The select nodes canbe maintained radially outwardly by a force originating from outside thehelical and reverse helical components. Thus, the structure can beformed without a traditional internal mandrel.

[0016] In accordance with another more detailed aspect of the presentinvention, the method can further include arranging a plurality ofcontinuous fibers to form a plurality of elongated strands in apredetermined orientation including at least two different strands withdifferent orientations that intersect one another at the nodes. Theplurality of fibers can be overlapped and consolidated at the nodes. Thefibers can be compacted at the nodes to reduce gaps. The fibers can beconsolidated by twisting the strands. In addition, the fibers can beconsolidated by wrapping other fibers around the strands to form a coreof substantially unidirectional fibers wrapped with a layer of outerfibers. In addition, the strands can be consolidated by braiding atleast one of the strands. Furthermore, the strands can be consolidatedby braiding other fibers around the strands to form a core ofsubstantially unidirectional fibers wrapped with a layer of outerbraided fibers.

[0017] An apparatus or machine for fabricating the structures includes aplurality of fiber feed sources to supply a plurality of continuousfibers and a puller to pull the continuous fibers from the fiber feedsources and through a processing path with a longitudinal axis. Aplurality of rotational elements are associated with the fiber feedsources and rotatable with respect to the processing path in oppositedirections around the longitudinal axis to wind the continuous fibers inopposite directions to form helical and reverse helical components whichintersect at nodes. A support frame is disposed along the processingpath and includes a plurality of engagement members to engage thehelical and reverse helical components path substantially only atlocations localized at the nodes in the processing path, and to maintainthe nodes of the helical and reverse helical components radiallyoutwardly from the longitudinal axis to form sequential discretesegments in the helical and reverse helical components. A resinapplicator applies resin to the continuous fibers.

[0018] In accordance with a more detailed aspect of the presentinvention, the support frame can be an external support frame disposedoutside the helical and reverse helical components.

[0019] The plurality of engagement members can be disposed around theprocessing path to engage the nodes from outside the helical and reversehelical components. Thus, the structure can be formed without atraditional internal mandrel.

[0020] As stated above, a three-dimensional structure can include aplurality of spaced-apart, helical components, each having a commonangular orientation and sequential discrete segments wrapping around thelongitudinal axis in one direction. The structure also can include aplurality of spaced-apart, reverse helical components, each having anopposite angular orientation with respect to the helical components, andsequential discrete segments wrapping around the longitudinal axis in anopposite direction. The helical and reverse helical components intersectat nodes. Furthermore, a plurality of longitudinal members can intersectthe helical and reverse helical components at the nodes, and can beoriented substantially parallel with the longitudinal axis. The helicaland reverse helical components and the longitudinal members are formedfrom a plurality of continuous fibers.

[0021] In accordance with a more detailed aspect of the presentinvention, at least some of the fibers can form at least portions of atleast two members from the group of the helical components, the reversehelical components, and the longitudinal members. Such fibers transitionat the nodes.

[0022] In accordance with another more detailed aspect of the presentinvention, at least some of the plurality of continuous fibers caninclude a core of elongated fibers and a sleeve of braided fiberssurrounding the core of elongated fibers.

[0023] Additional features and advantages of the invention will beapparent from the detailed description which follows, taken inconjunction with the accompanying drawings, which together illustrate,by way of example, features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a perspective view of an apparatus for fabricatingcomplex, composite structures in accordance with an embodiment of thepresent invention;

[0025]FIG. 2a is an end view of the apparatus of FIG. 1;

[0026]FIG. 2b is an end view of the apparatus of FIG. 1 with groups offibers reduced to a single representative fiber for clarity;

[0027]FIG. 3a is a partial perspective view of the apparatus of FIG. 1;

[0028]FIG. 3b is a partial end view of the apparatus of FIG. 1;

[0029]FIG. 4a is a side view of an exemplary structure to be fabricatedwith the apparatus of FIG. 1;

[0030]FIG. 4b is an end view of the exemplary structure of FIG. 4a;

[0031]FIG. 4c is a side view of an end of an exemplary structure of FIG.4a with an integral transition to a circular cross-section;

[0032]FIG. 4d is an end view of the exemplary structure of FIG. 4a withan exterior skin, shell or grid;

[0033]FIG. 4e is a side view of an exemplary structure to be fabricatedwith the apparatus of FIG. 1;

[0034]FIG. 4f is an end view of the exemplary structure of FIG. 4e;

[0035]FIG. 5a is a schematic end view of the apparatus of FIG. 1 showingtravel paths;

[0036]FIG. 5b-5 d are schematic end views of the apparatus of FIG. 1showing the operation of the apparatus;

[0037]FIG. 5e is a schematic end view of the apparatus of FIG. 1 showingtravel paths;

[0038]FIG. 6 is a schematic view of a portion of the apparatus of FIG. 1showing a pulling and cut-off mechanism;

[0039]FIG. 7 is a perspective view of a plurality of fibers twisted bythe apparatus of FIG. 1 in accordance with the present invention;

[0040]FIG. 8 is a perspective view of a plurality of fibers wrapped bythe apparatus of FIG. 1 in accordance with the present invention;

[0041]FIG. 9 is a perspective view of a plurality of fibers braided bythe apparatus of FIG. 1 in accordance with the present invention;

[0042]FIG. 9b is a perspective view of a sleeve of braided fiberssurrounding a core of fibers by the apparatus of FIG. 1 in accordancewith the present invention;

[0043]FIGS. 10a and b are partial perspective views of the structure ofFIGS. 4a and b, showing a node or intersection;

[0044]FIG. 10c is a cross sectional view of the structure of FIGS. 4aand 4 b showing an intersection;

[0045]FIG. 10d is a cross sectional view of the structure of FIGS. 4aand 4 b showing an intersection;

[0046]FIG. 10e is a partial side view of the structure of FIGS. 4a and 4b;

[0047]FIG. 10f is another partial side view of the structure of FIGS. 4aand 4 b showing an off-set intersection;

[0048]FIGS. 11a and b are side views of a structure fabricated inaccordance with the present invention without one of the regularlyoccurring nodes;

[0049]FIGS. 11c and d are side views of a structure fabricated inaccordance with the present invention without one of the regularlyoccurring nodes for attachment;

[0050]FIG. 11e is a partial side view of the structure of FIGS. 4a and 4b showing a node;

[0051]FIGS. 12a and b are side views of tapering structures fabricatedin accordance with the present invention;

[0052]FIG. 13 is a top view of an arcuate structure fabricated inaccordance with the present invention;

[0053]FIG. 14 is an end view of a structure fabricated in accordancewith the present invention;

[0054]FIG. 15 is a side view of a structure fabricated in accordancewith the present invention;

[0055]FIG. 16a is a perspective view of a rectangular structurefabricated in accordance with the present invention;

[0056]FIG. 16b is a top view of the rectangular structure of FIG. 16a;

[0057]FIG. 16c is a side view of the rectangular structure of FIG. 16a;

[0058]FIG. 16d is an end view of the rectangular structure of FIG. 16a;

[0059]FIG. 17a is a perspective view of a structure fabricated inaccordance with the present invention; and

[0060]FIG. 17b is a perspective view of the structure of FIG. 17a, shownwith a skin or shell.

DETAILED DESCRIPTION

[0061] Reference will now be made to the exemplary embodimentsillustrated in the drawings, and specific language will be used hereinto describe the same. It will nevertheless be understood that nolimitation of the scope of the invention is thereby intended.Alterations and further modifications of the inventive featuresillustrated herein, and additional applications of the principles of theinventions as illustrated herein, which would occur to one skilled inthe relevant art and having possession of this disclosure, are to beconsidered within the scope of the invention.

[0062] The present invention introduces a unique methodology referred toas tensioned fiber placement or casting, which has demonstratedsurprising utility for fabricating or casting complex, compositefiber/resin structures in free-space. The method involves interlacingone or more rotating strands of transverse fibers with an array oftensioned, longitudinal fibers to form a support skeleton suitable forfurther interlacing or over-wrapping of other fiber strands at varyingorientations. These collective, interwoven, fibers are coated with resinand cured in this tensioned, skeletal configuration to form a sturdystructure with very high load capacity and stiffness, but very lowweight. The open nature of the structure not only provides for minimalweight, but also is well suited for numerous and diverse structuralapplications. The skeletal or grid structure also may be covered withadditional structure or a non-structural skin.

[0063] The subject, tensioned fiber placement or casting method isimplemented with an apparatus 10, illustrated in FIGS. 1-3b, forfabricating complex, three-dimensional, composite structures.Three-dimensional truss structures are a specific example of a fieldthat may benefit from use of such an apparatus and method. For example,the apparatus 10 and method can be utilized to fabricate thethree-dimensional truss structures as disclosed in U.S. Pat. No.5,921,048, which is herein incorporated by reference, and similar orrelated structures. For illustrational purposes, the apparatus 10 andmethod shall be described herein with respect to fabricating an“eight-node” structure 12, as described below and illustrated in FIGS.4a and 4 b. It is of course understood that the apparatus 10 and methodof the present invention can be utilized to fabricate other structures,including for example, six or twelve-node structures (as described inU.S. Pat. No. 5,921,048), other n-node structures, etc.

[0064] Referring to FIGS. 4a and 4 b, the eight-node structure 12, aswell as other n-node structures, can be characterized by a plurality ofelements or members arranged in a repeating pattern along the length orlongitudinal axis 14 of the structure 12. The structure 12 can beconceptualized and described as a plurality of helical components 20wrapped or wound about the longitudinal axis 14 and forming a helixwrapping around the axis. Each helical component 20 is formed by aplurality of sequential discrete segments 22 coupled end-to-end in ahelical configuration. Each of the discrete segments 22 can be straightand oriented at an angle with respect to adjacent segments. Thus, eachhelix or helical component can be formed by sequential straightsegments. In one aspect, three or more of the straight segments 22 forma single, substantial complete rotation about the axis 14 creating apolygonal cross-sectional shape when viewed along the axis 14. Forexample, three segments forming a single complete rotation form atriangle; four segments forming a single complete rotation form a square(as shown) or rectangle; etc. A plurality of helical components orhelixes can be spaced-apart along the axis, so that the helicalcomponents or helixes are concentric, and intermesh. The various helicalcomponents intersect at external nodes 26 and internal nodes 28, asdescribed below.

[0065] In one aspect, the components 20 include: 1) a plurality ofspaced-apart, helical components 30, and 2) a plurality of spaced-apart,reverse helical components 34 attached to the helical components. Thehelical and reverse helical components 30 and 34 have a commonlongitudinal axis, but opposing angular orientations about the axis.Thus, the helical components 30 wrap around the axis in one direction,while the reverse helical components 32 wrap around the axis in theother direction. As stated above, the helical and reverse helicalcomponents 30 and 34 can intersect one another at internal and externalnodes 28 and 26. The straight segments 22 of the helical and reversehelical components 30 and 34 together form a first cross-sectional shapewhen viewed along the axis. For example, as described above; threesegments form a triangle; four segments form a square (as shown) orrectangle; etc.

[0066] In addition, the components 20 can further include: 3)spaced-apart, rotated helical components 38, and 4) spaced-apart,rotated reverse helical components 42, both of which are similar to, butrotated with respect to, the respective helical and reverse helicalcomponents 30 and 34. Similar to the helical and reverse helicalcomponents described above, the rotated helical and rotated reversehelical components 38 and 42 can wrap around the axis in oppositedirections. The straight segments 22 of the rotated helical and rotatedreverse helical components 38 and 42 form a second cross-sectional shapethat is rotated with respect to the first cross-sectional shape. Thesegments of the rotated and rotated reverse helical components, and thusthe second cross-sectional shape, are rotated about the axis withrespect to the helical and reverse helical components, and thus thefirst cross-sectional shape.

[0067] In one aspect, all of the helical components 20 include at leastthree, sequential straight segments 22 that form a single, substantiallycomplete rotation about the axis. For example, the helical components 20can include four, sequential straight segments 22 that form a single,substantially complete rotation about the axis 14, as shown. Thus, thefour straight segments 22 in each of the helical and reverse helicalcomponents 30 and 34 form a first, square cross-sectional shape.Similarly, the four straight segments of the rotated helical and rotatedreverse helical components 38 and 42 form a second, squarecross-sectional shape, that can be concentric with, but rotated withrespect to the first cross-sectional shape, to create an eight-pointedstar (as shown in FIG. 4b). The structure 12 thus has eight externalnodes 26.

[0068] In one aspect, the number of helical components 20 in each of thehelical, reverse helical, rotated helical, and rotated reverse helicalcomponents 30, 34, 38 and 42 is the same as the number of straightsegments in each component. Thus, the components 20 can include fourhelical components 30, four reverse helical components 34, four rotatedhelical components 38, and four rotated reverse helical components 42,for a total of sixteen helical components. As stated above, the fourcomponents in each of the helical, reverse helical, rotated helical, androtated reverse helical components are spaced-apart from one another sothat the structure has an open configuration with spaces between thecomponents.

[0069] In addition, straight or axial components may extendlongitudinally, and intersect the internal and/or external nodes 28 and26. For example, the structure 12 can include eight straight or axialinternal components 46 intersecting the eight internal nodes 28, asshown in FIGS. 4a and 4 b. Therefore, the structure 12 as shown includestwenty-four components. In addition, or alternatively, a structure caninclude eight straight or axial external components 47 intersecting theeight external nodes 26, as shown in FIGS. 4e and 4 f. The componentscan be formed of a composite fiber/resin with continuous fibersextending along the length of the components. The resulting structurehas been found to exhibit enhanced stiffness and load bearing capacityper unit weight.

[0070] It will be appreciated from an examination of the resultingstructure, however, that the complex configuration is difficult tomanufacture. For example, the straight segments extend between externalnodes 26, which are at a greater distance from the axis 14, and passthrough the structure at internal nodes 28, which are at a lesserdistance from the axis. The straight segments further add to thecomplexity of the structure because they laterally traverse the trussstructure surrounding an open, central core at various angles. Thesegments of one cross-sectional shape traverse the other cross-sectionalshape. Thus, the structure is difficult to easily, quickly, and costeffectively manufacture with conventional mandrel techniques.

[0071] Referring again to FIGS. 1-3b, the apparatus or machine 10 isshown for fabricating complex, composite structures, such as the trussstructures described above, from continuous fibers or tows 50 or strandsof fibers. As stated above, the apparatus 10 as shown is configured forfabricating the three-dimensional, eight-node truss structure 12described above. It is of course understood that the apparatus 10 can beconfigured to fabricate other such complex structures having differentconfigurations.

[0072] The apparatus 10 can include a frame or base support member 54with a processing path 58 along which the continuous fibers 50 arearranged into the complex structure 12. The processing path 58 can havea longitudinal axis that is concentric with the longitudinal axis 14 ofthe structure 12. The continuous fibers 50, and resulting structure 12,are drawn through the processing path 58 of the apparatus 10, asindicated by arrow 60. As discussed in greater detail below, a pullercan pull the continuous fibers 50 and/or structure 12 through theprocessing path 58 and maintain the fibers 50 in a taut condition. Thefibers 50 are disposed in the processing path 58, and pulled taut, toprovide an axial support configuration which forms an operating skeletonfor assembly of the structure 12. This skeletal structure enablesformation of complex open structures without dependence upon atraditional internal mandrel, die, or other internal shaping deviceconfigured to support the entire surface of an object. Again, it will beappreciated that such a traditional internal mandrel configured tosupport all such internal surfaces of such a complex three-dimensionalstructure would be difficult to remove from the structure.

[0073] A plurality of fiber feed sources 62 can be associated with orcoupled to the frame or base support member 54 to provide the continuousfibers 50. Thus, the continuous fibers 50 can be drawn from the fiberfeed sources 62 and through the apparatus 10 or processing path 58. Thefiber feed sources 62 can include center feed coils or outer feed spoolsabout which the continuous fibers 50 are wound. Any fiber source thatfacilitates continuous release of a tensioned fiber can be utilized inthis apparatus.

[0074] As shown in FIG. 2a, the apparatus 10 can include a separatefiber feed source 62 for each component. Thus, in this embodiment, theapparatus 10 includes twenty-four fiber feed sources 62 (four helicalsources 63 a, b, c & d; four reverse helical sources 64 a, b, c & d;four rotated helical sources 65 a, b, c & d; four rotated reversehelical sources 66 a, b, c & d; and eight straight sources 67 a, b, c,d, e, f, g & h, as shown in FIGS. 2a and 2 b). It is of courseunderstood that the number of fiber feed sources 62 depends on thenumber of components, which can vary depending on the configuration ofthe structure to be fabricated. The fiber feed sources 62 can be spacedaround the axis 14 at various inclinations and radially spaced positionsto facilitate drawing the fibers through the processing path.

[0075] In addition, each fiber feed source 62 can provide a plurality offibers or tows 50 that are grouped together in the strands to form theindividual components of the structure 12. For example, a single tow canbe formed of several thousand individual fibers. As discussed in greaterdetail below, the plurality of fibers or tows 50 from each fiber feedsource 62 can be twisted or rotated together (indicated by arrow 68),wrapped, braided, or overwrapped with a braid to form the strands.

[0076] A rotational or displacement element(s) can be associated withthe fiber feed sources 62 and frame or base support member 54 todisplace the fibers 50 or fiber feed sources 62 around the processingpath 58 or axis 14, as indicated by perimeter arrows 70 and 72. Therotational element(s) can include first and second rotational elementsrotatable with respect to the processing path 58 around the axis 14 inopposite directions 70 and 72 to wind the continuous fibers 50 inopposite directions to form the helical and reverse helical components30 and 34.

[0077] For example, the first rotational element can rotate the fourhelical sources 63 a, b, c & d (for the four helical components 30) in afirst direction 70, while the second rotational element can rotate fourreverse helical sources 64 a, b, c & d (for the four reverse helicalcomponents 34) in a second direction 72. The first rotational elementalso may rotate the four rotated helical sources 65 a, b, c & d in thefirst direction 70, while the second rotational element also may rotatethe four rotated reverse helical sources 66 a, b, c & d in the seconddirection 72. Alternatively, a third rotational element can rotate thefour rotated helical sources 65 a, b, c & d (for the four rotatedhelical components 38) in the first direction 70, while a fourthrotational element can rotate four rotated reverse helical sources 66 a,b, c & d (for the four rotated reverse helical components 42) in thesecond direction 72.

[0078] Referring to FIG. 5a, the first rotational element, or the fourhelical sources 63 a, b, c & d, can follow a first path 73 in the firstdirection 70, while the second rotational element, or the four rotatedhelical sources 64 a, b, c & d, can follow a second path 74 in thesecond direction 72. The paths 73 and 74 can share portions, but haveseparate portions where the fiber feed sources 62 can pass one anotherwhile traveling in different directions, as shown. Similarly, the thirdrotational element, or the four rotated helical sources 65 a, b, c & d,can follow a third path 75 in the first direction 70, while the fourthrotational element, or the four rotated reverse helical sources 66 a, b,c & d, can follow a fourth path 76 in the second direction 72.

[0079] The rotational element(s) can include tracks on the paths alongwhich the fiber feed sources 62 travel. The rotational element(s) caninclude rotating frames to which the fiber feed sources 62 are coupledso that the fiber feed sources also travel along the paths as therotating frames rotate.

[0080] Referring to FIGS. 5b-d, the first helical source 63 a is shownrotating about the axis 14 (FIGS. 1-2b) in the first direction 70 withthe fibers graphically illustrated in bolded format. Similarly, thefirst rotated helical source 65 a is shown rotating about the axis inthe first direction 70 with the fibers graphically illustrated in dashedand bolded format.

[0081] As shown and described above, the tracks or paths along which thefiber feed sources travel can be substantially circular. Alternatively,the tracks or paths can be straighter or more square or rectangular.Referring to FIG. 5e, an alternative configuration of the paths ortracks of the rotational elements or fiber feed sources is shown. Thepaths or tracks can have a straighter configuration that more closelyresembles the cross-sectional shape of the structure being formed.

[0082] Referring again to FIG. 1, an orientation guide member 77 can beassociated with the frame or base support member 54 and positionedbetween the fiber feed sources 62 and the processing path 58 to receivethe continuous fibers 50 from the plurality of fiber feed sources 62 forangularly reorienting the continuous fibers 50 to a desiredpre-processing configuration about the axis 14. The orientation guidemember can be a ring for guiding the fibers 50 from the fiber feedsources 62 to the processing path 58. The preprocessing configurationrepresents the reorientation of the fibers 50 from the feed sources 62to a longitudinally stressed skeletal structure along the processingpath 58.

[0083] An intermediate support element or member 80 can be disposed atthe processing path 58 and associated with the frame or base supportmember 54. The intermediate support element 80 can include a pluralityof engagement members 84 disposed around the processing path 58 toengage the nodes, such as the external nodes 26 of the components 20,and to direct and maintain the nodes 26 of the components 20 radiallyoutwardly from the longitudinal axis 14. Thus, the intermediate supportelement 80 and/or engagement members 84 form the sequential discrete orstraight segments 22 in the helical and reverse helical components 30and 34. The intermediate support element 80 and/or engagement members 84support the fibers 50 in the configuration of the structure 12. Asdiscussed in greater detail below, the engagement members 84 can travelwith the structure 12 as the fibers 50 are drawn through the processingpath 58. The engagement members 84 and/or intermediate support element80 also can be a puller or traction member to pull the fibers throughthe processing path, as described below. The intermediate supportelement 80 can be disposed around the structure 12 with the engagementmembers 84 engaging the nodes 26 from the exterior of the structure 12,as shown. The engagement members 84 can include hooks, notches, orgrooved heads around which the fibers 50 are wound. The engagementmembers 84 and/or intermediate support element 80 form an externalsupport structure for the fibers, as opposed to a traditional internalmandrel configured to support the entire inner surface of the structure.

[0084] The engagement members 84 can engage or contact the structuresubstantially only at the nodes. The engagement or contact can belocalized at or along the nodes. The engagement members 84 can bias thenodes radially outwardly from the longitudinal axis. Thus, theengagement members 84 can exert a radial force on the structure at thenodes. The engagement members 84 form the straight segments in thestructure. The engagement members 84 can establish free space pointsintermittently which operate to support the nodes of the structurewithout a traditional internal mandrel that is continuous.

[0085] The intermediate support element 80 and/or engagement members 84can be radially displacable and operable with respect to the fibers 50to intermitently draw or displace fibers 50 from the axial supportconfiguration and along a radial path with respect to the elongate axis14 to a stable, extended position representing the three-dimensionalstructure 12. Thus, the configuration of the structure 12 or operatingskeleton can be maintained without the aid of an internal mandrel orcavity die.

[0086] The intermediate support element 80 and/or engagement members 84can be located radially outwardly to correspond to the desired size ordiameter of the structure 12. In one aspect, the engagement members 84are adjustably positioned with respect to the axis 14 so that astructure 12 of any desired size or diameter can be formed. Theintermediate support element 80 and/or the engagement members 84 can bedisplaced radially outwardly during processing so that changes indiameter can be accomplished during processing.

[0087] The engagement members 84 can be provided in sets or groupscorresponding to the number of nodes. For example, the intermediatesupport element 80 can have eight sets of engagement members 84corresponding to the eight nodes 26 of the structure 12. In one aspect,the number of sets can be adjustable to correspond to the desired numberof nodes. In another aspect, numerous sets can be provided, with onlysome being used depending on the number of desired nodes.

[0088] The adjustable nature of the engagement members 84 and/or supportelement 80 can provide for easier manufacture of geometry specifictooling. It will be appreciated that minor changes made to traditionalstructures requires that a new mandrel be machined.

[0089] As described above, the intermediate support element 80 and/orengagement members 84 can support and maintain the fibers from outsidethe structure. Thus, the intermediate support element 80 and/orengagement members 84 do not interfere with the various segments thatcross or intersect the interior of the structure. As discussed above, atraditional, internal, continuous mandrel can be difficult to withdrawfrom the interior of the structure because of the segments that cross orintersect the interior. In another aspect, the intermediate supportstructure or engagement members alternatively can be disposed in theinterior of the structure. The engagement members would still onlyengage or contact the structure substantially only at the nodes, asdescribed above. The engagement members disposed inside the structurecan provide a non-continuous interior support. The engagement memberscan move along the processing path, and can pivot or displace inwardlyat the end of the processing path to avoid interference with thecrossing or intersecting segments of the structure. Such a configurationcan be useful for larger diameter structures that can allow more room inthe interior.

[0090] A resin applicator 90 can be associated with the frame or basesupport member 54 to apply resin to the continuous fibers 50, as isknown in the art. The resin applicator 90 can include a nozzle to sprayor drip resin onto the fibers. The resin can be applied to the fibers 50while the fibers 50 are supported by the engagement members 84. Inaddition, the resin can be applied to the fibers 50 prior to engagementby the engagement members 84 so that the engagement members do not blockthe application of the resin. A nozzle or spraying is one example ofmeans for applying resin to the fibers. Other means for applying resinto the fibers include, for example, a resin bath through which thefibers are drawn, multiple spray nozzles, prepreg (pre-impregnated)fibers, etc. Applying the resin to the fibers creates a liquidresin/fiber composite.

[0091] An oven, heat source, or other curing device 96 can be associatedwith the frame or base support member 54 to help cure the resin, as isknown in the art. The resin can be cured while the fibers 50 aresupported by the engagement members 84. An oven or heat source is oneexample of means for curing the resin or the liquid fiber/resincomposite. Other means for curing the resin include, for example, heat,forced air, UV radiation, microwaves, electron beam, laser beam, etc.Curing the resin or liquid resin/fiber composite creates a sturdy,rigid, three-dimensional truss structure capable of bearingmultidirectional loading.

[0092] Referring to FIG. 6, a puller or traction member can beassociated with the frame or the base support member 54 to apply axialtension and pull the continuous fibers 50 and/or the structure 12through the processing path 58. The puller also can engage the curedresin/fiber composite structure, such as with the use of a gear-likedevice 100 with teeth that intermesh with the cured structure. Thepuller also can engage the structure with graspers 102 that grasp thestructure or components, such as the axial components. The graspers canbe pneumatically, hydraulically, electrically or mechanically actuated.As stated above, as the structure 12 and fibers 50 are pulled throughthe processing path 58, the engagement members 84 and/or intermediatesupport element 80 can move with the structure 12. In one aspect, theengagement members 84 can move along the intermediate support element80. In another aspect, the engagement members 84 also can be used as thepuller or traction member. Thus, the structure 12 can be fabricated withany desired length, while at the same time having variable radialdimensions.

[0093] A cutter 110 also can be associated with the frame or basesupport member 54 to cut the structure 12 to a desired length. Thecutter 110 can include a blade to cut through the various componentsand/or segments, and may be operated along any transverse orientationwith respect to the longitudinal axis 14. In addition, the cutter caninclude a high-pressure fluid jet, water jet, laser beam, or any othercutting mechanism.

[0094] The fibers of the various components (helical, reverse helical,and straight/axial) intersect and/or overlap. In both cases, gaps canresult between the individual fibers or tows, and reduce the strength ofthe component, segment, or total structure by up to 90%. The apparatus10 advantageously can include mechanisms to reduce the gaps by twisting,wrapping, and/or braiding the fibers together. FIGS. 7-9 show fibersthat have been twisted, wrapped and braided, respectively.

[0095] The apparatus 10 can include a twisting member to twist(indicated by arrow 68 in FIGS. 1 and 2a) the plurality of fibers 50from a fiber feed source 62 together. The twisting member can be coupledbetween the rotational element and the fiber feed source 62, and cantwist the fiber feed source 62. In addition, the twisting member caninclude the fiber feed source 62 being rotatably coupled to therotational element or frame. The twisting member is twistable to cause aplurality of adjacent fibers to twist around one another and reduce orprevent any gaps between the fibers, as shown in FIG. 7.

[0096] In addition, the apparatus can include a wrapping member to wrapa group of fibers. The wrapping member can be associated with the fiberfeed source 62 and/or the rotational element. The wrapping member can berotatable around a plurality of fibers to wrap the plurality of fiberswith another plurality of fibers to reduce or prevent any gaps betweenthe fibers. In addition, as shown in FIG. 2a, the fiber feed source 62can include an inner fiber feed source 136, and an outer fiber feedsource 138. The outer fiber feed source 138 can rotate (indicated byarrow 68 in FIGS. 1 and 2a) about the inner fiber feed source so thatouter fibers from the outer fiber feed source are wrapped around innerfibers from the inner fiber feed source. Thus, the wrapping member canform a core 140 of substantially straight fibers 50 surrounded by alayer of wrapped fibers 142, as shown in FIG. 8.

[0097] In addition, the apparatus can include a braiding mechanism tobraid the fibers 160 together. The braiding mechanism can include thefiber feed sources 62 configured to interweave with one another. Thefiber feed sources 62 can be configured to separate the plurality offibers 50 or tows, as shown in FIG. 2a, such that the fibers or tows canbe passed through or between one another to braid or interweave thefibers. Thus, the fibers in the various fiber feed sources can traverseone another and/or intersect one another to form a braid, as shown inFIG. 9.

[0098] In addition, a braided sleeve 162 can encapsulate a core ofstraight or twisted fibers 163, as shown in FIG. 9b. The apparatus caninclude a braiding mechanism to rotate around a plurality of fibers towrap the plurality of fibers with another braided plurality of fibers.Inner and outer fiber feed sources can be provided with the outer fiberreed source including the braiding mechanism.

[0099] Referring to FIGS. 10a-c, the interwoven relationship of fibersis illustrated at an internal node 28 of the structure 12 beingfabricated. It will be appreciated that the internal node illustrated inthe figures can be representative of any intersection or any node in thestructure. The helical component 30, reverse helical component 34, andstraight or axial internal member 46 intersect at the internal node 28.As stated above, the fibers 50 of the components 30, 34 and 46 canoverlap one another. Specifically, as shown in FIGS. 10a and c, thefibers 50 of the helical and reverse helical components 30 and 34 canpass between the fibers 50 of the straight or axial component 46. It isof course understood that the fibers 50 of all the components can passbetween the fibers of other components. For example, the fibers or towsfrom a fiber feed source, such as straight or axial feed source 67 a inFIG. 2a, can be separated a sufficient distance so that the fibers orother fiber feed source can pass therethrough, such as helical andreverse helical feed sources 64 a and 65 a in FIG. 2a. In addition, itis understood that the components can merely pass by one another. Theoverlaying or intersecting fibers, however, can form gaps between thefibers. As previously mentioned, such gaps can reduce the strength ofthe structure by as much as 90%. It will be appreciated that thestrength of the structure is derived from the synergy of the collectivefibers as a bundle. Thus, isolating or separating fibers has adetrimental effect on the strength of the structure. The fibers 50 ofthe components 30, 34 and/or 46 advantageously can be twisted, wrapped,braided, or wrapped with a braid as described above, to condense thefibers and reduce any gaps, and increase the strength of the fibers, andthe structure.

[0100] Alternatively, the relationship of the fibers of the nodes orintersections of the components can have other configurations. Referringto FIG. 10c, the helical component 30, reverse helical component 34, andstraight or axial internal member 46 intersect at the internal node 28.The fibers of the axial internal member 46 can be maintained in a singletow or strand with the fibers of the helical and reverse helicalcomponents 30 and 34 surrounding the axial internal member 46. Thus, theaxial internal member 46 intersects the helical or reverse helicalmembers 30 and 34. Therefore, the fibers of the axial internal member 46are maintained together in a substantially straight configuration, andwithout gaps. The fibers or tows from a fiber feed source, such ashelical and reverse helical feed sources 64 a and 65 a in FIG. 2a, canbe separated to pass around the fibers or other fiber feed source, suchas straight or axial feed source 67 a in FIG. 2a. It will be appreciatedthat the helical and reverse helical components 30 and 34 can similarlybe maintained together, with the axial member 46 surrounding them.

[0101] Referring to FIG. 10e, the helical component 30, reverse helicalcomponent 34, and straight or axial internal member 46 can intersect atthe internal node 28 that is in a single location. While the componentshave been described above as intersecting at a node, it will beappreciated that the intersection of many fibers can create a bulkynode, and may introduce gaps. In addition, the intersection of the manyfibers can create nonlinearities in the fibers that also degrade theirstructural performance. In one aspect, the nodes or intersections can beoff-set with respect to one another. Thus, the nodes or intersectionscan be off-set, or spaced apart, forming a grouping of different nodesor intersections in close proximity to one another. Referring to FIG.10f, the helical component 30, reverse helical component 34, andinternal member 46 can intersect at different locations, thus forming aplurality of nodes or intersections in close proximity to one another.The helical and reverse helical components 30 and 34 can intersect oneanother at one node 28 a. The helical component 30 can intersect theaxial internal member 46 at another node 28 b, while the reverse helicalcomponent 34 can intersect at another node 28 c. Thus, a single node orpoint of intersection can be separated into two or more nodes orintersections to reduce the bulk of the intersections and to reducegaps.

[0102] The apparatus 10 also can be configured to create structureswithout one or more of the nodes. Referring to FIGS. 11a and 11 b,another truss structure 200 is shown which has been fabricated without anode at one of the regular intervals, indicated at 202. Such aconfiguration provides a flatter area against the structure 200 whichcan facilitate connecting another truss structure or object 203 to thestructure 200, as shown in FIGS. 11c and 11 d. As stated above, it isdesirable to form the structure from continuous fibers to preserve thestrength of the structure. While such a node can be cut from astructure, doing so cuts the fibers, and can reduce the strength of thefibers, components, and/or structure. The structure 200 shown, however,has been formed without a node, but with continuous fibers. Thestructure 200 has been formed by changing the regular direction ororientation of some of the components, such as the helical and reversehelical components that would have formed the node. For example, onereverse helical component 204, shown in bold, is shown wrapping aroundthe structure in the second direction 72, then continuing longitudinallyalong one of the straight or axial components 46, then wrapping aroundthe structure in the first direction 70. It will be appreciated that thecorresponding helical component can be similarly reoriented. Thus, thereverse helical component 204 reverses directions to become a helicalcomponent 206. To form the structure 200, the corresponding fiber feedsources can have their directions reversed.

[0103] The truss structure 200 illustrated in FIGS. 11a and b also isexemplary of another type of truss structure in which one or moresingle, continuous fibers or strands form two or more differentcomponents of the structure. For example, as shown in FIGS. 11a and b, asingle, continuous fiber or strand is shown forming three differentcomponents of the structure, namely a reverse helical component 204, astraight or axial component 46, and a helical component 206. The single,continuous fiber or strand, thus transitions from one component toanother at a transitional node 207. Transitioning the fibers or strandsbetween several components can have several advantages. For example,transitioning the fibers can increase the number or percentage of fibersis certain desired components, while reducing the number or percentageof fibers in other components, to add strength to the desiredcomponents, and thus tailor the structure to the desired application orknown stress or load concentrations. In addition, transitioning thefibers also can change the orientation of the fibers at desired nodes toalign the fibers in desired directions to take advantage of theproperties of the fibers. For example, it will be appreciated thatintersecting a plurality of fibers can cause stress or loading to beplaced between the fibers, where they are weaker, rather than along thefibers themselves, where they are stronger. Thus, transitioning thefibers can reorient the fibers so that intersecting fibers apply stressor loading against the fibers, and increase the strength of thestructure.

[0104] The apparatus 10 can be configured to provide other means forfacilitating connection to the resulting structure. For example,referring to FIG. 11e, a node 210 can be formed with an aperture or bore212 therein. Such a bore 212 in the resulting structure can receive abolt or the like to secure another object to the structure. The bore 212can be formed by wrapping the fibers or helical and reverse helicalcomponents 30 and 34 around a peg or rod. Such a peg or rod can be partof the engagement member 84. For example, the engagement member 84 caninclude a hook about which the components 30 and 34 are wrapped. Thehook itself can form the resulting bore. Alternatively, a separate pegor rod can be used. The peg or rod can be threaded to form a threadedbore.

[0105] In addition, the subject method and apparatus can be configuredto form structures with a taper. Referring to FIGS. 12a and 12 b,tapering structures 220 and 224 are shown which taper in eitherdirection. The tapering structures 220 and 224 can be formed byconfiguring an intermediate support element 226, and/or engagementmembers 228, in a tapering configuration. The engagement members 228 canbe located closer or further from the axis 14 in order to create thetapering structures 220 and 224. The intermediate support element 228can move with the structures along the processing path. Both of thestructures 220 and 224 can be made sequentially to form a continuousstructure.

[0106] In addition, the subject method and apparatus can be configuredto form a curved structure 240, with an arcuate axis 242, as in FIG. 13.The apparatus can include an arcuate processing path. The engagementmembers 244 on the inside of the arc can be located closer together,while the engagement members 246 on the outside of the arc can belocated further apart from one another. This disparity in fiberpositioning can be applied to form parts having a variety of radii.

[0107] In addition, the apparatus can be configured to formnon-symmetrical structures. The engagement members can be configured toachieve the desired configuration of the structure. The engagementmembers 84 were shown in FIG. 1 as being symmetrically located aroundthe axis 14 to fabricate a symmetrical structure. For example, referringto FIG. 14, the engagement members 280 can be arranged elliptically, orin an elliptical shape, to form a structure 282 with a more ellipticalconfiguration or cross-section. It will be appreciated that other shapescan be formed, such as airfoil shapes, etc.

[0108] In another aspect, the subject method and apparatus can beconfigured to form tapered components, such as tapered external members300 that taper along their length, as shown in FIG. 15. Such a structure304 can be formed with tapered strands 300 that are thicker and strongerat one end or portion of the structure, and thinner and lighter atanother end or portion. The fiber feed sources can be configured toincrease or reduce the number of fibers in the strand or tow to form thetaper.

[0109] In another aspect, the subject method and apparatus can beconfigured to form a structure 330 with a square or rectangularcross-section, as shown in FIG. 16a-d. The structure 330 includes sixexternal nodes 334 configured to form the square cross-section. Forexample, the external support frame and/or engagement members can bepositioned with three sets of engagement members at the top of thestructure, and three sets at the bottom.

[0110] In another aspect, the subject method and apparatus can beconfigured to form a multi-node structure 350, as shown in FIGS. 17a andb, that begins to resemble a circle or tube that can include an exteriorskin, shell or grid 354.

[0111] Referring again to FIGS. 1-5d, the tensioned fiber placement orcasting method for fabricating complex, three-dimensional structuresfrom composite fiber/resin is shown using the apparatus 10. A pluralityof continuous fibers is pulled through and along a processing path witha longitudinal axis. The fibers can be pulled from one or more feedsources. As described above, the fibers can be pulled by a puller thatengages the fibers and advances them through the preprocessingconfiguration and processing stage, and into the final cured structure.

[0112] At least some of the fibers are wound around the longitudinalaxis in opposite directions to form 1) helical components, and 2)reverse helical components, that intersect at nodes. In addition, someof the fibers can be wound around the longitudinal axis in oppositedirections and different orientations to form 3) rotated helicalcomponents, and 4) rotated reverse helical components. As describedabove, the fiber sources can be rotated around the axis and along thepaths with variable lengths and changing orientations.

[0113] The plurality of continuous fibers is arranged into a skeletonstructure having a desired configuration for realizing a predeterminedstructure. The skeleton includes: 1) continuous straight strandsoriented along the processing path and spaced apart from thelongitudinal axis; 2) helical strands with sequential discrete orstraight segments wrapping around the longitudinal axis in onedirection; and 3) reverse helical strands with sequential discrete orstraight segments wrapping around the longitudinal axis in anotheropposite direction, with the helical and reverse helical strandsintersecting at nodes. The skeleton can also include rotated helicalcomponents, and rotated reverse helical components.

[0114] The helical and reverse helical components can be directed orforced radially outwardly from the longitudinal axis at the nodes toform the sequential discrete or straight segments in the helical andreverse helical components.

[0115] Select nodes are engaged and positioned, such as by engagementmembers of an intermediate support element, to maintain the straightsegments in correct orientations. The select nodes are directed radiallyoutwardly from the longitudinal axis to create sequential straightsegments in the helical and reverse helical components (and the rotatedhelical and rotated reverse helical components) with the nodes being ata greater distance from the longitudinal axis than the remainingsegments. In one aspect, the nodes are engaged and maintained fromoutside the helical and reverse helical components.

[0116] The skeleton is simultaneously pulled along the processing pathwhile the continuous fibers are arranged, woven, laced, braided,covered, displaced to nodal positions, stabilized, and cured. Theseoperations are sequentially or concurrently applied as the skeletonadvances along the processing path. Resin is applied to the continuousfibers prior to or during the preprocessing configuration to thoroughlywet all of the fibers. As described above, the resin can by applied byapplicators, such as spray nozzles. The resin is cured, such as by ovensor other devices as described above.

[0117] In addition, the plurality of continuous fibers can be arrangedto form a plurality of elongated strands in a predetermined orientation,including at least two different strands with different orientationsthat intersect one another at a node. The plurality of fibers isoverlapped at the node, often forming gaps between the plurality offibers. Accordingly, the plurality of fibers in each strand isconsolidated together to compact the fibers together and reduce thegaps. The step of consolidating the fibers in each strand together caninclude twisting the strand, wrapping other fibers around the strand toform a core of substantially unidirectional fibers wrapped with a layerof outer fibers, braiding the strands together, and/or braiding outerfibers around straight or twisted inner fibers.

[0118] In addition, fibers or tows can be begun or terminated withineach component, member or strand to reduce or increase the number ofstrands along the length thereof, or along the length of the structure.Thus, the diameter or size of a strand, component or member can increaseor decrease along its length, or the length of the structure. It will beappreciated that the number of fibers affects the strength of thestructure. It also will be appreciated that some applications requirediffering strengths along the length of the structure. For example, fora utility pole, greater load bearing capability can be required at thebase, while less load bearing capability may be required at the top.

[0119] The apparatus or process can be started with a first, greaterplurality of fibers, and reduce or discontinue the number of fibers ortows as the process continues. For example, each fiber feed source caninclude a plurality of fiber feed sources, or can provide a plurality offibers. Select fiber feed sources within the plurality of fiber feedsources forming a strand or component can be terminated, or the fibersor tows cut, to reduce the number of fibers or tows in the strand orcomponent. Thus, the strand or component can have a greater number offibers or tows at one end, and thus greater load bearing capability, andhave a lesser number of fibers or tows at another end, and thus lesserload bearing capability. Alternatively, the apparatus or process can bestarted with a second, lesser plurality of fibers, and increase or addfibers or tows as the process continues.

[0120] Referring to FIG. 4c, it can be desirable to integrally form thetruss structure 12 with a different configuration. Such differentconfiguration can facilitate connecting the end of the structure toanother object. For example, the structure 12 can be integrally formedwith an end 300 having tubular or cylindrical cross-sectional shape. Theapparatus 10 can include a mandrel, as is known in the art, which can beinserted into the apparatus 10 to form such different configurations.For example, a mandrel with a circular cross-sectional shape can beinserted into the apparatus 10. The fibers 50 from the fiber feedsources can be wrapped around the mandrel to form the end 300 with thetubular or cylindrical cross-sectional shape. The operation of theintermediate support member 80 and/or engagement members 84 may besuspended while the mandrel is in the apparatus 10 so that the fiberscan be wrapped around the mandrel. It is of course understood that othershapes can be formed at the end.

[0121] Referring to FIG. 4d, it can be desirable to form the trussstructure 12 with an exterior skin, shell or grid 310. The skin or shellcan close the structure 12. The skin or shell also can be formed ofcomposite fiber/resin. The apparatus 10 can wrap a plurality of fibersaround the truss structure 12 in a continuous layer. The apparatus 10can wrap the structure 12 in a second stage, after the structure hasbeen formed, due to the intermediate support member 80 and/or engagementmember 84 being disposed about the exterior of the structure.Alternatively, the apparatus 10 can wrap the structure 12 while thestructure is being formed, such as when the intermediate support memberand/or engagement members disposed in the interior of the structure.

[0122] As stated above, the fibers preferably are continuous, and can becarbon, glass, basalt, aramid, or other fibers. The resin can be anytype, such as a thermoplastic resin, like PCV, or thermoset resin, likeepoxy or vinyl ester.

[0123] As stated above, the tensioned fiber casting method and apparatuscan be configured for any type of structure by tensioning fibers into askeletal, open structure. In addition, the method and apparatusdescribed above also can be used to fabricate greneral polygonalcross-section stiffened structures, such as isogrid structures.

[0124] It is to be understood that the above-referenced arrangements areillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements can bedevised without departing from the spirit and scope of the presentinvention while the present invention has been shown in the drawings anddescribed above in connection with the exemplary embodiments(s) of theinvention. It will be apparent to those of ordinary skill in the artthat numerous modifications can be made without departing from theprinciples and concepts of the invention as set forth in the claims.

What is claimed is:
 1. A method for fabricating a complex,three-dimensional structure from composite fiber/resin, comprising thesteps of: a) pulling a plurality of continuous fibers from a feed sourcealong a processing path about a longitudinal axis; b) winding at leastsome of the fibers around the longitudinal axis in opposite directionsto form helical and reverse helical components that intersect at nodes;c) engaging the fibers in the processing path substantially only atlocations localized at select nodes without substantially engaging thehelical and reverse helical components; d) maintaining the select nodesradially outwardly from the longitudinal axis to create sequentialdiscrete segments in the helical and reverse helical components; e)applying a resin to the fibers; and f) curing the resin.
 2. A method inaccordance with claim 1, wherein the step of engaging the select nodesfurther includes engaging the select nodes from outside the helical andreverse helical components; and wherein the step of maintaining theselect nodes further includes maintaining the select nodes radiallyoutwardly by a force originating from outside the helical and reversehelical components.
 3. A method in accordance with claim 1, wherein thestep of maintaining further includes the step of displacing the selectnodes radially outwardly from the longitudinal axis.
 4. A method inaccordance with claim 1, wherein the step of maintaining furtherincludes maintaining the fibers in a desired configuration without usingan internal mandrel disposed inside an interior space defined by thehelical and reverse helical components.
 5. A method in accordance withclaim 1, further comprising the step of: arranging a plurality ofcontinuous fibers into a skeleton structure having a desiredconfiguration, including at least: 1) continuous straight strandsoriented along the processing path and spaced apart from thelongitudinal axis; 2) helical strands with sequential discrete segmentswrapping around the longitudinal axis in one direction; and 3) reversehelical strands with sequential discrete segments wrapping around thelongitudinal axis in another opposite direction, with the helical andreverse helical strands intersecting at nodes.
 6. A method in accordancewith claim 1, further comprising the step of: a) guiding the pluralityof continuous fibers along the processing path and around thelongitudinal axis in opposite directions to form: 1) at least two,spaced apart, helical components each having a common angularorientation about the longitudinal axis, and 2) at least one reversehelical component, attached to the at least two helical componentshaving an opposing angular orientation with respect to the two helicalcomponents; and wherein engaging and maintaining the nodes forms atleast three elongate, discrete segments sequentially connected end toend in a helical configuration forming a single, substantially completerotation about the longitudinal axis.
 7. A method in accordance withclaim 1, further comprising the step of arranging a plurality ofcontinuous fibers into a skeleton structure having a desiredconfiguration.
 8. A method in accordance with claim 7, furthercomprising the step of simultaneously pulling the skeleton structurealong the processing path while arranging the continuous fibers.
 9. Amethod in accordance with claim 1, further comprising the step of: a)guiding other of the plurality of continuous fibers along the processingpath and the longitudinal axis substantially parallel with thelongitudinal axis to form longitudinal components; and b) intersectingthe helical, reverse helical, and longitudinal components at internalnodes.
 10. A method in accordance with claim 1, further comprising thestep of: a) guiding other of the plurality of continuous fibers alongthe processing path and the longitudinal axis substantially parallelwith the longitudinal axis to form longitudinal components; and b)intersecting the helical, reverse helical, and longitudinal componentsat external nodes.
 11. A method in accordance with claim 1, furthercomprising the step of: a) arranging a plurality of continuous fibers toform a plurality of elongated strands in a predetermined orientationincluding at least two different strands with different orientationsthat intersect one another at at least one of the nodes; b) overlappingthe plurality of fibers at the node; and c) consolidating the pluralityof fibers in each strand together.
 12. A method in accordance with claim11, wherein the step of overlapping the plurality of fibers at the nodesincludes forming gaps between the plurality of fibers; and wherein thestep of consolidating the plurality of fibers includes compacting thefibers together and reducing the gaps.
 13. A method in accordance withclaim 11, wherein the step of consolidating the fibers in each strandtogether includes twisting at least one of the strands.
 14. A method inaccordance with claim 11, wherein the step of consolidating the fibersin each strand together includes: wrapping other fibers around at leastone of the strands to form a core of substantially unidirectional fiberswrapped with a layer of outer fibers.
 15. A method in accordance withclaim 11, wherein the step of consolidating the fibers in each strandtogether includes braiding at least one of the strands.
 16. A method inaccordance with claim 11, wherein the step of consolidating the fibersin each strand together includes: braiding other fibers around at leastone of the strands to form a core of substantially unidirectional fiberswrapped with a layer of outer braided fibers.
 17. An apparatus forfabricating a complex, three-dimensional structure from compositefiber/resin, the apparatus comprising: a) a plurality of fiber feedsources to supply a plurality of continuous fibers; b) a puller to pullthe continuous fibers from the fiber feed sources; c) a processing pathdefined between the plurality of fiber feed sources and the puller andhaving a longitudinal axis; d) a plurality of rotational elements,associated with the fiber feed sources, rotatable with respect to theprocessing path in opposite directions around the longitudinal axis towind the continuous fibers in opposite directions to form helical andreverse helical components which intersect at nodes; e) a support frame,disposed along the processing path, including a plurality of engagementmembers to engage the helical and reverse helical components pathsubstantially only at locations localized at the nodes in the processingpath, and to maintain the nodes of the helical and reverse helicalcomponents radially outwardly from the longitudinal axis to formsequential discrete segments in the helical and reverse helicalcomponents; and f) a resin applicator to apply resin to the continuousfibers.
 18. A device in accordance with claim 17, wherein the supportframe includes an external support frame disposed outside the helicaland reverse helical components; and wherein the plurality of engagementmembers are disposed around the processing path to engage the nodes fromoutside the helical and reverse helical components.
 19. A device inaccordance with claim 17, further comprising a twisting member,associated with the rotational element, twistable to cause a pluralityof adjacent fibers to twist around one another.
 20. A device inaccordance with claim 17, further comprising a wrapping member,associated with the rotational element, rotatable around a plurality offibers to wrap the plurality of fibers with another plurality of fibersto form a core of substantially straight fibers surrounded by a layer ofwrapped fibers.
 21. A device in accordance with claim 17, furthercomprising a braiding member, associated with the rotational element, tointertwine a plurality of fibers into a braided strand.
 22. A device inaccordance with claim 17, wherein the engagement members are displacableradially outwardly from the longitudinal axis to displace the nodesradially outwardly.
 23. A device in accordance with claim 17, whereinthe continuous fibers are maintained in a desired configuration in theprocessing path by the engagement members without the use of an internalmandrel.
 24. A machine for fabricating complex, three-dimensional trussassemblies from substantially straight, composite fiber/resin segmentsformed by winding continuous lengths of fiber between node points whichdefine predetermined angular reorientation of the segments throughhelical rotations about an elongate axis of the truss assembly, saidmachine comprising: a) a base support member including a plurality offiber feed sources mounted to the base support member, at least one ofthe fiber feed sources including a rotational element which permits therotational element and associated feed source to displace angularly withrespect to the elongate axis while feeding fiber for processing in themachine; b) an orientation guide member positioned adjacent the basesupport member to receive an array of continuous fibers from theplurality of fiber feed sources and angularly reorient the array ofcontinuous fibers to a desired pre-processing configuration about theelongate axis; c) a traction member to pull the array of continuousfibers along a processing path formed about the elongate axis subsequentto the pre-processing configuration and maintain at least a portion ofthe fibers in a taut condition along the processing path to provide anaxial and radial support configuration which forms an operating skeletonstructure for the three-dimensional truss assembly; and d) at least oneintermediate, radially displacable support element positioned betweenthe base support and the traction member and operable with respect tothe array of fibers to intermitently displace at least one fiber fromthe axial support configuration and along a radial path with respect tothe elongate axis to a stable, extended position representing thethree-dimensional truss assembly, said truss assembly being maintainedabout the operating skeleton structure in a stable truss configurationwithout aid of an internal mandrel or cavity die; e) means for applyinguncured resin to the array of fibers prior to repositioning in theprocessing path to form a liquid fiber/resin composite; and f) means forcuring the liquid fiber/resin composite while in the stable trussconfiguration to develop a sturdy three-dimensional truss assemblycapable of bearing multidirectional loading.
 25. A three-dimensionalstructure with a longitudinal axis, comprising: a) a plurality ofspaced-apart, helical components each having a common angularorientation and sequential discrete segments wrapping around thelongitudinal axis in one direction; b) a plurality of spaced-apart,reverse helical components each having an opposite angular orientationwith respect to the helical components, and sequential discrete segmentswrapping around the longitudinal axis in an opposite direction, with thehelical and reverse helical components intersecting at nodes; c) aplurality of longitudinal members, intersecting the helical and reversehelical components at the nodes, and oriented substantially parallelwith the longitudinal axis; d) the helical and reverse helicalcomponents and the longitudinal members being formed from a plurality ofcontinuous fibers; and e) at least some of the fibers forming portionsof at least two of the helical and reverse helical components andlongitudinal members, such fibers transitioning at the nodes between atleast two members of the group consisting of: the helical components,the reverse helical components, and the longitudinal members.
 26. Athree-dimensional structure with a longitudinal axis, comprising: a) aplurality of spaced-apart, helical components each having a commonangular orientation and sequential discrete segments wrapping around thelongitudinal axis in one direction; b) a plurality of spaced-apart,reverse helical components each having an opposite angular orientationwith respect to the helical components, and sequential discrete segmentswrapping around the longitudinal axis in another opposite direction,with the helical and reverse helical components intersecting at nodes;c) the helical and reverse helical components being formed from aplurality of continuous fibers; and d) at least some of the plurality ofcontinuous fibers including a core of elongated fibers and a sleeve ofbraided fibers surrounding the core of elongated fibers.
 27. A structurein accordance with claim 26, wherein the intersection of the helical andreverse helical components at nodes tends to form gaps between thefibers at the nodes; and wherein the sleeve of braided fibers compressesthe core of elongated fibers together to reduce the gaps.